1. Field of the Invention
The present invention relates to a structure for a vertical displacement and a method for fabricating the same, and more particularly to a MEMS silicon structure.
2. Description of the Related Art
Generally, a structure for the vertical displacement provides an upper electrode and a bottom electrode horizontally disposed and detects a change in a capacitance therebetween due to a vertical displacement.
For the fabrication of the structure, a plurality of patterning procedures must be conducted because the structure member and the electrodes cannot be manufactured at the same time. Also, to maintain a predetermined interval between the electrodes, there may be required a sacrificial layer or a layer attachment, which makes the fabrication complicated. Furthermore, to precisely detect the vertical displacement, the interval between electrodes must be small, which results in a stiction therebetween.
It is an object of the present invention to provide a structure for detecting a vertical displacement wherein the structure member and the electrodes are manufactured simultaneously, thereby simplifying the fabrication procedures and also the electrodes are disposed laterally, thereby being free from a stiction phenomenon.
The other object of the invention is to provide a fabrication method for the same.
To achieve the above objects of the invention, there is provided a structure for detecting a vertical displacement comprising a body, an inertial mass floated over the body, a plurality of support beams extending from the inertial mass so as to suspend the inertial mass over the body, movable electrodes integrally formed with the inertial mass, and fixed electrodes floated over the body, each being positioned between the neighboring movable electrodes, wherein a vertical length of the movable electrode is different from a vertical length of the fixed electrode.
In the case of using the support beams as torsional members, the inertial mass has different density between a first side portion thereof and a second side portion thereof so as to make a rotation centered about the support beams. Preferably, the vertical lengths of the movable electrodes are shorter than the vertical lengths of the fixed electrodes or vice versa.
In the case of using the support beams as bending members, the vertical lengths of the movable electrodes located at a first side portion of the inertial mass are longer than the vertical lengths of neighboring fixed electrodes, and the vertical lengths of the movable electrodes located at a second side portion of the inertial mass are shorter than the vertical lengths of neighboring fixed electrodes, the first and second side portions being oppositely positioned centered about the bending members.
Within the various embodiments, the body is made of a single crystal silicon wafer or of a SOI wafer including a silicon substrate, an insulating layer and a silicon layer, the inertial mass is fabricated by etching the silicon layer. When using a SOI wafer, the silicon substrate is made of single crystal silicon or epitaxial growth polysilicon.
Alternatively, the body can be made of a SOG wafer including glass and silicon layer, the inertial mass is fabricated by etching the silicon layer.